[Sema] PR32953: Fix hard crash of implicit instantiation of undefined template preceeded by scoped variable

[hintonda]

Summary

Reset ScopeSpec when parsing class, struct, etc.. Fixes PR32953.

lib/Parse/ParseDecl.cpp

#include "clang/Basic/OpenCLImageTypes.def"
     // class-specifier:
     case tok::kw_class:
     case tok::kw_struct:
     case tok::kw___interface:
     case tok::kw_union: {
       tok::TokenKind Kind = Tok.getKind();
       ConsumeToken();
 
+      DS.getTypeSpecScope() = CXXScopeSpec();
+
       // These are attributes following class specifiers.
       // To produce better diagnostic, we parse them when
       // parsing class specifier.
       ParsedAttributesWithRange Attributes(AttrFactory);
       ParseClassSpecifier(Kind, Loc, DS, TemplateInfo, AS,
                           EnteringContext, DSContext, Attributes);
 
       // If there are attributes following class specifier,

test/SemaTemplate/instantiate-complete.cpp

namespace pr7199 {
   template <class T> class A; // expected-note {{template is declared here}}
   template <class T> class B {
     class A<T>::C field; // expected-error {{implicit instantiation of undefined template 'pr7199::A<int>'}}
   };
 
   template class B<int>; // expected-note {{in instantiation}}
 }
 
+namespace PR32953 {
+  struct bar {};
+  template <typename A> struct Temp; // expected-note {{template is declared here}}
+  PR32953::bar struct Temp<int>::foo(); // expected-error {{implicit instantiation of undefined template 'PR32953::Temp<int>'}} \
+                                         expected-error {{cannot combine with previous 'type-name' declaration specifier}} \
+                                         expected-error {{expected unqualified-id}}
+}
+
 namespace PR8425 {
   template <typename T>
   class BaseT {};
 
   template <typename T>
   class DerivedT : public BaseT<T> {};
 
   template <typename T>